1. Field of the Invention
The present invention relates to an ejection device for a mass-containing package including at least one piston rod having a toothing extending along a longitudinal extent of the piston rod, and a drive unit for displacing the at least one piston rod and including at least one gear wheel engageable with the toothing of the at least one piston rod, and a drive motor for driving the at least one gear wheel.
2. Description of the Prior Art
An ejection device of the type described, which is also called a rack dispenser, is used for forcing out from a package such as, e.g., a film bag or a cartridge, the mass, which is packaged therein, at the mass application site. The ejection devices of this type are suitable for forcing out from a package different types of masses, such as, e.g., mortar mass or sealing mass. Upon actuation of the drive motor, the piston rod is pushed a predetermined amount, so that a pressure plate, which is arranged on the piston rod, acts on the package, and a corresponding amount of the mass enclosed in the package, is forced out through an outlet opening in the head portion of the ejection device. For changing the package, from which the mass contained therein has to be ejected, the piston rod should be withdrawn in order to be able to remove the spent package from the ejection device and replace it with another package.
German Publication DE 22 27 930 A1 discloses an ejection device of the above-described type and including piston rod having a toothing extending along a longitudinal extent of the piston rod, and a drive unit for displacing the piston rod and including a gear wheel engageable with the toothing of the piston rod, and drive means, which is formed of a motor and a gear unit, for driving the gear wheel.
The displaced piston rod is returned in its initial position by reversal the motor pols. After the piston rod has been returned to its position, the located in the ejection device, spent package is removed, and a new package is placed into the ejection device.
The drawback of the ejection device which is disclosed in DE 22 27 930 A1, consists in that the return of the piston rod in its initial position is time-consuming.
An ejection device is also disclosed in German Publication DE 35 35 291 A1. In this ejection device, the toothing of the piston rod is disengaged from the gear wheel by rotating the piston rod about its longitudinal axis. This provides for a free displacement of the piston rod.
The drawback of the ejection device of DE 35 35 229 A1 consists in that the disengagement of the piston rod from the gear wheel is rather sluggish and is associated with high wear of the components.
Accordingly, an object of the present invention is to provide an ejection device of the type described above in which a simple and low-wear disengagement of the gear wheel form the piston rod is possible.